You can set privilege for the role “User” to control the user’s access to leads. If this setting is enabled, then all the accounts with role “User” will only be able to view the leads that are assigned to them instead of the default view of showing all leads.

To enable access control, click on Settings from the top bar,

Click on User Management option from the left menu and then click on the Access Control option to turn on this setting.

Now when you go to the lead details page, you will find an option called Manage Access which can be used to allow additional users to view the leads.